Hydrogen water is regular water that's been enhanced with molecular hydrogen gas, known as H2. Hydrogen is a tasteless, colorless, odorless gas that can combine with other elements, such as oxygen. Regular water is made up of three atoms: One oxygen and two hydrogen. That's why you see water called "H2O." Hydrogen is said to have certain benefits. The theory is that adding the extra H2 to water will improve your health. The research thus far on hydrogen water's health benefits is limited. Manufacturers sometimes sell hydrogen water bottled with the gas already added to it. You also can buy systems to make hydrogen water at home, similar to the products that carbonate regular water. Hydrogen water is also called hydrogen-rich water and hydrogenated water.